To cooperate treasonably, as with an enemy occupation force in one’s country.

There are two definitions of Collaboration. The newer, assumed, definition that harkens images of employees floating amongst cubicles, surreptitiously contributing to dozens of projects, never staying too long as to not waste time, but always helping out just enough to make a difference.

Then there is what your grandfather would think about if you mentioned the word collaboration to him. Citizens in an occupied territory helping the occupier to advance their own goals.